With the advent of higher prices for the energy the world consumes, much interest has been generated in new sources of energy and in more efficient uses of this energy. One of the energy conversion devices for which promise has been held is the magnetohydrodynamic generator (MHD). The basis for the operation of an MHD is that passing an electrically conducting fluid through a strong magnetic field will produce an electric potential between opposite sides of the throat through which the conducting fluid flows. The magnitude of the power generated with a given fluid is proportional to the velocity of the fluid through the throat.
MHD development has typically focused on the use of high temperature, high pressure gas or plasma, although some systems have been developed using an electrically conducting liquid. The temperature of the plasma or liquid used in these devices is usually on the order of several hundred to a few thousand degrees Celsius. The pressure under which the working fluid operates is also very high in most systems, on the order of several hundred to a few thousand pounds per square inch. The use of such high temperature and pressure fluids limits the choice of materials out of which the system can be made. The high temperatures and high pressures in these systems also make the systems prone to leaks and contribute to the rapid deterioration of machinery such as pumps used in the system.
To provide the flow of conducting fluid through the MHD throat, some systems have incorporated means for establishing a convective flow of the fluid around a closed loop. This convective flow is established by heating the fluid at one point in the loop and cooling it at another. Such a system is shown in U.S. Pat. No. 3,375,664 to Wells. It has been found, though, that the low velocity thus obtained has not been sufficient to permit the MHD to generate more than a few milliwatts of power even with vertical leg members up to 100 feet tall. Another means of causing a flow of the conducting fluid through an MHD loop has been to establish a convective flow by introducing a gas into part of the loop to create a density differential between the fluid in different sections of the loop. This has typically been accomplished by boiling either the conducting liquid or a second fluid and using the vapor bubbles to leviate one column of the fluid. A system that operates in this manner is disclosed in U.S. Pat. No. 3,443,129 to Hammitt. Such systems, however, have been troublesome, since boiling the fluid takes thermal energy from the system, reducing the heat in the conducting fluid in the rising column. Also, the height and temperature of the rising column are severely constrained by the need to prevent condensation of the gas bubbles before they reach the top of the column.